A man can row a boat with 8 km/h in still water. He is crossing a river of width 8 km, where the speed of water flow is 4 km/h. What direction should he head the boat to cross the river in the shortest time?

(1) 30° with the current

(2) 60° with the current

(3) 90° with the current

(4) 120° with the current

The horizontal range of a particle thrown from the ground is four times the maximum height. The angle of projection with the vertical is:

(1) 60°

(2) 30°

(3) 45°

(4) 90°

A particle is moving 30° north of east with speed 6 m/s. After 3 s the particle is found to be moving along north at the same speed. The magnitude of average acceleration in this interval of time is

(1) 1 $\mathrm{m}/{\mathrm{s}}^2$

(2) 6 $\mathrm{m}/{\mathrm{s}}^2$

(3) Zero

(4) 2 $\mathrm{m}/{\mathrm{s}}^2$

A particle is thrown with a velocity of 40 m/s. If it passes A and B as shown in the figure at time ${\mathrm{t}}_1$ = 1 s and ${\mathrm{t}}_2$ = 3 s. The value of h is:

(1) 15 m

(2) 10 m

(3) 30 m

(4) 20 m

At a certain moment, the angle between the velocity vector $\overrightarrow{\mathrm{v}}$ and the acceleration $\overrightarrow{\mathrm{a}}$ of a particle is greater than 90°. What can be inferred about its motion at that moment?

(1) It moves along a curve and its speed is decreasing.

(2) It moves along a straight line and accelerated.

(3) It moves along a curve and its speed is increasing.

(4) It moves along a straight line and it is decelerated.

To a stationary man, the rain is falling on his back with a velocity v at an angle $\mathrm{\theta }$ with vertical. To make the rain-velocity perpendicular to the man, he:

(1) must move forward with a velocity vsin$\mathrm{\theta }$.

(2) must move forward with a velocity vtan$\mathrm{\theta }$.

(3) must move forward with a velocity vcos$\mathrm{\theta }$.

(4) should move in the backward direction.

A particle is thrown from the ground with a speed of 20 m/s at an angle 60° above the horizontal. Average velocity over its entire journey just before hitting the ground is:

(1) 10 m/s

(2) 20 m/s

(3) Zero

(4) 15 m/s

A person can throw a ball up to a maximum horizontal range of \(400~\text{m}\). The maximum height to which he can throw the ball is:
1. \(200~\text{m}\)
2. \(100~\text{m}\)
3. \(150~\text{m}\)
4. \(250~\text{m}\)

A particle is moving on a circular path of radius 1 m with a speed of 10 m/s. The magnitude of change in its velocity in the interval it subtends an angle 60° at the center is:

1. 10 m/s

2. 20 m/s

3. $20\sqrt{2}$ m/s

4. Zero

A car is moving along east at 10 m/s and a bus is moving along north at 10 m/s. The velocity of the car with respect to the bus is along: